Insulating Basement Wall


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Old 10-16-12, 11:23 AM
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Insulating Basement Wall

Hi... I am new to this and had a question about insulating my basement. Right now I have 1" foam board insulation up against the concrete wall and sealed the seams with Tyvek tape. Then I have the framing over that so it holds the boards against the wall. My question is if I use fiberglass insulation between the studs should I use faced or unfaced?

Thanks in advance!
Nick
 
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Old 10-16-12, 12:27 PM
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Hi Nick and welcome to the forum.
Basements are one of the toughest areas of a home to improve. Moisture in the ground outside will always be working its way towards the dryer inside, even if the walls looked dry when you started, the vapor was simply drying before it accumulated to where it looked wet. If it can continue through to the inside it will not accumulate. If it is blocked by a vapor barrier, it will accumulate until it matches the moisture content of the soil outside. And there is the question, how moist is the soil around your house. Given your state (not Nevada) it grows grass so it has moisture and that moisture behind a vapor barrier on the inside can potentially grow things.

However, if your foam board is the typical pink or blue, not foil faced, then it will allow a small amount of moisture vapor to pass, called a vapor diffusion retarder: Vapor Barriers or Vapor Diffusion Retarders | Department of Energy
If this is what you have, then using an unfaced batt insulation will allow that small amount of moisture vapor to continue through and not build up to where there is a problem.

If you have water of any kind, that is too much to expect it to pass through the one inch of rigid foam and efforts should be made to eliminate the water from the outside.

Be aware, without extreme measures, basements can be done wrong and turn out right. They can also be done right and turn out wrong. Many variables.

Bud
 
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Old 10-16-12, 07:00 PM
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Thanks for the response Bud... I have the 1" pink foamular board so it makes sense to go with unfaced batt insulation and no other vapor barrier.
 
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Old 10-17-12, 05:38 AM
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That is one approach but I recommend lots of reading. The link below and the links at the bottom of that article and subsequent links from those will provide more information than you ever wanted.

As I stated above, basements are tough and opinions will vary, partly because basements vary and part because they are still trying to figure out what works. An example would be the dew point on your wall. With the fiberglass insulation allowing some warm humid air to infiltrate through to the surface of that pink foam, where you have r-5 plus the concrete to the outside and r-13 to the inside, that foam will be cold (above grade). Will it form condensation, I don't know. Switch to mineral wool (Roxul for example) and being extremely dense it would reduce the chances or air flow, thus less condensation potential.

Lots of variables. Be sure to air seal and insulate the areas above the foundation (rim joist) and especially where it rests on the top of the foundation.

Bud

BSD-103: Understanding Basements — Building Science Information
 
 

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